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IJSRST173164 | Received: 10 Feb-2017 | Accepted : 22-Feb-2017 | January-February-2017 [(3)1: 341-351 ]
© 2017 IJSRST | Volume 3 | Issue 1 | Print ISSN: 2395-6011 | Online ISSN: 2395-602X Themed Section: Science and Technology
341
Accurate Position Control of Pneumatic Actuator Using On/Off Solenoid Valve
D. Venkatesa Prabu#1, A. Sathishkumar#2, C. Manibalaji#3, T. Sakthivel#4, V. Robin#5 #1,2
Assistant Professor, Department of Mechatronics Engineering, Mahendra College of Engineering, Salem, Tamilnadu, India #3,4,5
UG Scholar, Department of Mechatronics Engineering, Mahendra College of Engineering,Salem,Tamilnadu, India
ABSTRACT
paper deals with accurate positioning of pneumatic actuator using solenoid controller to development a fast,
accurate, and inexpensive position-controlled that may be applied to a variety of practical positioning applications
are described. A Pulse Width Modulation PWM valve pulsing algorithm to allow the on/off solenoid valves to use in
the place of costly servo valve. The open-loop characteristic is shown both theoretically and experimentally in near
the symmetrical. A comparison of the open- and closed-loop responses of standard PWM techniques and that the
PWM technique shows there has been a significant improvement in control. A linear process model is obtained from
experimental data using system identification. A intelligent controller of proportional integrative PI controller with
position feed forward. A state feedback controller with position, velocity and acceleration feedback as a continuous
controller. Proportional integral derivative PID controller with added friction compensation and position controlled
pneumatic actuator using Pulse Width Modulation PWM valve pulsing algorithms are described. The system
consists a standard double acting cylinder controlled with two three-way solenoid valves through a 12-bit A/D PC
board. It is using a non-linear motion of pneumatic actuator to control the plunger positioning it can be analyzed
through the displacement or potentiometer sensor.
Keywords: PWM, PID Controller, SMC, VAC, LVQNN, MPWM, FRL
I. INTRODUCTION
A Cylinder and Cartesian robots require linear position
control of their actuators to perform their task.
Pneumatic actuators offer several advantages for
positioning applications as low cost, high power to
weight ratio, ease to maintenance & cleanliness. So there
is particularly well suited for those applications where
speed and lightweight are critical. Unfortunately
pneumatic actuators are subject to high friction forces,
dead band due and dead time due to the compressibility
of the air. These non-line arities make accurate position
control for a pneumatic actuator is difficult to achieve.
As a result, a considerable amount of research work has
been devoted the development in various position
control systems for pneumatic actuators and use
expansive proportional servo valves and pressure sensor
feedback loops. The particularity of this application is
that, differently from previous works, there is not a
mathematical system model to tune the controller
parameters the tuning is made on field using a
experimental tuning procedure. The results obtained
using this position control system are satisfactory and
show a low value for position error and rise time without
the necessity of realizing complex non-linear mode. As a
result, a considerable amount of research has been
devoted to the development of various position control
systems in pneumatic actuators. Many of systems,
thought successful, use expensive proportional servo
valves and pressure sensor feedback loops and the
external loads are also assumed to be constant or slowly
varying.
II. METHODS AND MATERIAL
A. Pressure Relief Valve
The pressure relief valve (PRV) is used to control or
limit the pressure in a system or vessel which can build
up for a process upset, instrument or equipment is
failure. The pressure is relieved by allowing the
pressurized fluid flow from an auxiliary passage out of
the system. The relief valve is designed or set to open at
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342
a predetermined protect pressure vessels and other
equipment from being subjected that exceed their
design limits. When the set pressure is exceeded, the
relief valve becomes the path of least resistance as the
valve is forced open and a portion fluid is diverted
through the auxiliary route the pressure inside the vessel
will stop rising. Once it reaches the valve reseating
pressure valve will close. The blow down is usually
stated as a percentage of pressure and refers to how
much pressure needs to drop before the valve reseats.
The blow down can vary from roughly 2–20%, and
some valves are adjustable blow downs.
In high-pressure gas systems, is recommended the outlet
of the relief valve is open air. In systems where the
outlet is connected in piping, the opening relief valve
will give a pressure build up in the piping system and
downstream of the relief valve. This often means that
relief valve will not re-seat once the set pressure is
reached. For systems are called "differential" relief
valves are used. This means the pressure is only working
on area that is much smaller than the opening area of the
valve. If valve is opened and the pressure has to
decrease enormously before the valve closes the outlet
pressure of valve can easily keep the valve open.
Another consideration that if relief valves are connected
to the outlet pipe system, they may open as the pressure
in exhaust.
B. Double Acting Cylinder
A double-acting cylinder is an working the fluid acts are
alternately on both sides of the piston is shown in Fig
1.2.
In order to connect the piston in a double-acting cylinder
an external mechanism, such as a crank shaft, hole must
be provided in one end of the cylinder for the piston rod
and this is fitted with a gland or 'stuffing box' to prevent
escape of the working fuid.
Figure 1. Double Acting Cylinder
Double-acting cylinders are common in steam engines
but unusual in other engine types. Many hydraulic and
pneumatic cylinders use them needed to produce a force
are both directions. A double-acting hydraulic cylinder
port at each end, supplied with hydraulic fluid for both
retraction and extension of the piston. A double-acting
cylinder is used an external force is not available to
retract the piston or where high force is required in both
directions of travel.
C. PID Controller
A proportional integral derivative controller. The PID
controller is a control loop feedback mechanism
controller commonly used in industrial control systems.
A PID controller continuously calculates the error value
as difference between a desired set point and measured
process variable. The controller attempts to minimize the
error over time by adjustment of a control variable, such
as position of control valve and damper or the power
supplied to a heating element, to a new value determined
by a weighted sum.
Figure 2. PID Controller
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Where Kp, Ki, Kd all non-negative, denote the
coefficients for a proportional, integral, and derivative
terms, respectively sometimes denoted P, I, and D is
shown in Fig 1.3. As PID controller relies only on the
measured process variable are not an knowledge of the
underlying process, it has broadly applicable. By tuning
the three parameters of the model, a PID controller can
deal with specific process requirement. The response of
a controller can be described in terms of its
responsiveness to an error, the degree to which the
system overshoots a set point, and the degree of any
system oscillation. The use of PID algorithm does not
guarantee optimal control of the system or even its
stability.
D. Implementing PID Controller
Intelligent control for an electro-hydraulic actuator such
as neural networks was proposed for adaptive control
which consists of two BP networks and SMC using
recurrent high order sliding mode neural networks.
Figure 3. Developing PID Controller
Meanwhile, ANN-based PID control was developed to
reach high precision of tracking control of an electro-
hydraulic actuator is shown in Fig 1.3 Recently, fuzzy
logic control has been actively researched and utilized
such as fuzzy-PID controller by combining the merits of
fuzzy and conventional, self-tuning fuzzy linear control
to improve the robustness and hybrid control of fuzzy
and PID, Fuzzy-PD control with stability equation which
makes the systems being stable and robust.
E. Implementing PID Controller in Pneumatic
Actuator
The PID controller of the two spool type of servo
mechanism in two-stage Electro Hydraulic Servo Valve
under loaded condition has been develop. The model
consist of the interconnection between the Actuator
positioning stage, spool dynamics, chamber pressure
dynamics, output flow and load dynamics
relationship. The model has been implemented using
SOLIDWORKS link and Simulation - Pneumatics. The
proposed model can be used to predict performance and
to provide insights for improving the design of the valve.
Improved performances of this relatively in expensive
servo valve, either through improve physical design, or
through the advance control, can potentially expand the
use of electro hydraulics in cost constrained application.
F. FRL Unit
A pneumatic lubricator injects an aerosolized stream of
oil into the air line provide lubrication to internal
working parts of pneumatic tools, and other devices such
as actuating cylinders, valves and motors.
Compressed air enters in the inlet port passes over a
needle valve orifice attached to a pick-up tube. This tube
- often equipped with a sintered bronze filter - is
submerged into the reservoir bowl filled with light
machine oil. Oil is pulled up the venturi effect, and
emitted as an aerosol at the outlet port. The needle valve
is typically situated within a clear polycarbonate or
nylon housing to aid the oil flow rate adjustment. Some
Compressor oils and external chemicals can cause
polycarbonate or nylon sight glass to be degraded and
create the safety hazard.
A lubricator should always to be the last element in
FRL Filter-Regulator-Lubricator unit. If an FRL is
connected "backwards" with incoming air connected to
the lubricator, oil-laden air interferes in pressure
regulator operation, oil is separated from the air stream
and drained by the filter, and very little or none is
delivered to connected equipment.
Figure 4. 6 FRL unit
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G. ON/OFF Solenoid Valve
There are many valve design variations. The ordinary
valves can many ports and fluid paths. A 2-way valve,
for example, has 2 ports; if the valve is open, then the
two ports are connected to fluid may flow between the
ports; if the valve is closed then ports are isolated. If
valve is open when the solenoid is not energized, then
the valve is termed normally open (N.O.). Similarly, if
valve is closed when the solenoid is not energized, then
the valve is termed normally closed. There are also 3-
way and more complicated designs. A 3-way valve has 3
ports; it connects one port to either the two other ports
typically a supply port and an exhaust port. Solenoid
valves are also characterized by how they operate. A
small solenoid can generate the limited force. If force is
sufficient to open and close the valve, then a direct
acting solenoid valve is possible. An approximate
relationship between the required solenoid force Fs, the
fluid pressure P, and the orifice area of direct acting
solenoid value. (Fs PA Pπd2)
Where d is the orifice diameter. The typical solenoid
force might be 15 N (3.4 lbf). An application might be
the low pressure (e.g., 10 psi (69 kPa)) gas with a small
orifice diameter (e.g., 3⁄8 in (9.5 mm) for an orifice area
of 0.11 in2 (7.1×10−5 m2) and approximate force of 1.1
lbf (4.9 N)).
The solenoid valve is small black box at the top of photo
with input air line small green tube used to actuate a
larger rack and pinion actuator gray box which controls
the water pipe valve. When high pressures and large
orifices are encounter, then high force are required. To
generate the forces are internally piloted solenoid valve
design may be possible. In such a design line pressure is
used to generate the high valve forces; a small solenoid
controls how the line pressure is used. Internally piloted
valves are used in dishwashers and irrigation systems
where the fluid is water and pressure might be 80
pounds per square inch (550 kPa) the orifice diameter
might be 3⁄4 in (19 mm). In some solenoid valves the
solenoid acts directly on the main valve. Others use in a
small complete solenoid valve is known as a pilot, to
actuate a larger valve. While the second type is actually
a solenoid valve combined with pneumatically actuated
valve, they are sold and packaged as a single unit
referred to the solenoid valve. Piloted valves require
much less power to control, but they are noticeably
slower. Piloted solenoid usually need full power at all
time to open and stay, where the direct acting solenoid
may only need full power for a short period of time to
open it, and only low power to hold on. A direct acting
solenoid valve operates in 5 to 10 milliseconds. The
operation time of a pilot valve is depends on its size;
typical values are 15 to 150 milliseconds.
Figure 5. ON/OFF Solenoid Valve
The power consumption and supply requirements of
solenoid vary with application, being primarily
determined by fluid pressure and line diameter. For
example, a popular 3/4" 150 psi sprinkler valve, and
intended for 24 VAC (50 - 60 Hz) residential systems,
has a momentary inrush of 7.2 VA, and a holding power
requirement of 4.6 VA. Comparatively, an industrial
1/2" 10000 psi valve is intended for 12, 24, or 120 VAC
systems are in high pressure fluid and cryogenic
applications, it has an inrush of 300 VA and a holding
power of 22 VA. Neither valve lists a minimum pressure
required to remain closed in un-powered state.
The solenoid valve is an electromechanically operated
valve. The valve is an controlled by electric current
through a solenoid: in the case of two-port valve flow is
switched on or off; in the case of three-port valve, the
outflow is switched between two outlet ports. The
multiple solenoid valves can be placed together on a
manifold. Solenoid valves are the most frequently used
control elements in fluid. The tasks are to shut off,
release, and distribute or mix fluids. They are found in
many application areas. Solenoids offer fast and safe
switching, high reliability or long service life, good
medium compatibility of the materials are used. If has
low control power and compact design. The plunger-
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type actuator is used most frequently, pivoted-armature
actuators and rocker actuators are also used.
H. Foot Pedal Valve
A pedal from the Latin pes, pedis, meaning 'foot' is a
lever activated by the one's foot, sometimes called a
"foot pedal" but all pedals are used by a foot.
1. Transport
Pedals in road vehicles, see Car controls Pedals Bicycle
pedal, any set of levers which drive the rotation of a gear
train Pedal a small boat, usually used for recreational
purposes, powered by pedals Rudder pedals on aircraft,
see Rudder &Aircraft rudders, a campaign group in
Nottingham, England.
2. Electronic equipment
Foot pedals are often used to control playback
transcribers are used in medical transcription.
Footmouse, a foot-operated in computer mouse
3. Geometry
Pedal triangle is obtained by projecting a point
onto the sides of a triangle
Pedal curve is derived by construction from a
given curve is used in a pedal bin
Figure 6. Foot Pedal Valve
A sustain pedal or sustaining pedal also called damper
pedal, or open pedal is the most commonly used pedal in
a modern piano. It is typically to rightmost of two or
three pedals. When pressed the sustain pedal damped
strings on the piano is moving all the dampers are away
from the strings and allowing them to vibrate freely. All
the notes played will continue to sound until the
vibration naturally ceases, or until pedal is released.
The pianist sustain notes would be out of reach, for
instance in accompanying chord and accomplish legato
passages smoothly connected notes which have no
possible fingering otherwise. Raising the sustain pedal is
also causes of all the strings to vibrate sympathetically
in whichever notes are being played, which greatly
enriches the piano's tone.
A device similar to the sustain pedal effect was invented
by the piano pioneer Gottfried Silbermann it has
operated by the player's hands rather than a pedal. The
later eminent early builder, Johann Andreas Stein, may
have been the first to allow the player in lift the dampers
while still playing; his device was controlled by a knee
lever.
4. Specifying pedalling in musical compositions
Appropriate use of the pedal is often to the musician's
discretion, but composers and music editors are also use
pedal marks to notate it. The most common symbol for
this is a horizontal line below the grand staff, which lift
up and down with the pedal. An alternative or older
notation is the used to indicating the sustain pedal
should be depressed, and asterisk showing should be
lifted. Occasionally is general direction at the start of a
movement instructing that sustain pedal to be applied
continuously throughout. This may be marked with
senza sordini in without dampers are the similar wording.
In General MIDI, the sustain pedal information is
controlled by Control Change number.
5. Sostenuto Pedal
The sostenuto pedal is a similar device that sustain only
notes which are depressed at the time of pedal is
depressed. It is the usual middle of three pedals but in
some upright pianos the middle pedal instead lowers a
veil of felt between the hammers and the strings for
quiet practising.
6. Half Pedaling
For mechanical pianos it is possible to press down the
sustain pedal only partially such that the dampers just
touch the strings are very slightly. This technique are
advanced pianist is called half pedaling and allows a fine
variation of the sound. It can be observed that with half
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pedaling the damping is more effective for the higher
tones. A musical piece that is played with half pedaling
by some pianists is Beethoven's Moonlight Sonata. Most
recent digital pianos also support this effect.
7. Other Instruments
The electronic keyboards are include a sustain pedal, a
simple foot-operated switch which controls the
electronic or digital synthesis to produce a sustain effect.
Several recent models are used in more sophisticated
pedals that have a variable resistance, allowing half
pedaling. Vibraphones have sustain pedals are allow
from metal bars to ring. Some tubular bells have a
sustain pedal. The Cimbalom has a sustain are damper
pedal which allows its strings to ring or abruptly mutes
them.
Table 1. DCV Specification
Model
3Fm210-M5 3F210-06
3FM210-06
3F210-08
3FM210-08
Type 3port2position
Fluid Air(to be filtered by 40µ filter
element)
Operating Direct acting
Port size M5 1/8 ¼
Pressure range 0-8.bar (o-0.08Mpa)(0-
114Psi)
Temperature range -5-60c
Lubrication Not required
I. Literature Review
Intelligent switching control of pneumatic actuator
using on/off solenoid valves (KyoungkwanAhn a 2005)
[1]
The position control was successfully implemented
using on/off solenoid valves instead in expensive servo
valves. The valves were pulsed using a modified PWM
algorithm which compensated for the dead-time of
on/off valves. This was verified by experiments of
position control in which steady state errors were
reduced to within0.2 mm. The second contribution of
this paper was to apply the learning vector quantization
neural network (LVQNN) as a supervisor of switching
controllers in pneumatic servo systems with on/off valve,
where the LVQNN function to classifyed condition of
the external load and selects suitable gains of controller
for each weight condition. From the experiments of
position control of pneumatic cylinder are verified that
the proposed MPWM and smooth switching algorithm
were very effective to overcome deterioration control
performance of transient respons due to four different
load conditions and abrupt changes external loads.
Experimenting and modelling the dynamics of
pneumatic actuators are controlled by the pulse
width modulation (PWM) technique Arcangelo
( Messina a2005) [2]
An experimental investigation has been carried out in
detail with regard in pneumatic actuators controlled by
on-off solenoid valves whose opening and closing time
response is based on a pulse width modulation (PWM)
technique. The experimental set-up has provid evidence
an excellent repeatability along with a noise
superimposed on the displacement versus time having a
band less than 0.10 mm.
A mathematical model has to been proposed for
designing procedures and control strategies within the
frame pneumatic position. The mathematical model has
been tested and validated through several analytical or
experimental comparisons are excellent behaviour has
been obtained. The validation have consist in evaluation
of four flow-rate characteristics per valve for normal and
abnormal flow conditions and evaluation of the
kinematic law of opening and closing on-off valve
through a laser sensor estimation of the delays between
the logic electronic command and the mechanical law of
opening and closing on-off valves correlation between
real displacement and acceleration of rod and
displacement acceleration is obtained from the analytical
models respect to ten experimental tests used in only one
tuning parameter viscous coefficient tuned on one
measured displacement versus time on a trial and error
basis.
The analytical/experimental comparisons have shown
the ability of theoretical model to provide an accurate
mean expectation of the position of the actuator in less
than about 2 mm for five cycles over all in ten
experimental tests. Due the fact of a feedback normally
works with a sampling frequency corresponding to only
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one cycle, the mentioned performance of the model can
be considered attractive especially aimed at applying the
same model designing and tuning control strategies
based on ratings required from the particular application.
Numerical deviation have been provided in order to test
possible future models with the model presented here.
Experimental tests on positions control on a
pneumatic actuator using on/off solenoid valves
( A.Gentile', N 2002) [3]
An application developed in the Mechatronics
Laboratory is presented. It is a fast, accurate and
inexpensive position-controlled pneumatic actuator that
may he applied to a variety of practical positioning
applications. The position control was implemented
using solenoid valves driven by a novel PWM algorithm
and a experimental tuning method for the controller was
successfully adopted. The performances of the system
were investigated through experimental tests under a
variety of conditions. These varied conditions were
system mass, input type step, multi steps or ramp and
flow control settings on and wide open. The
performances obtained are satisfactory compared with
the results found in literature and they constitute a label
for the system to he surpassed in the future. The
actuator‟s performance is comparable to that achieved
by other researchers using servo valves. Current work in
this area is focused on the improvement of the system
performances using higher control strategy: traditional
PID with gain scheduling, adaptive or fuzzy control.
Accurate Sliding Mode Control in Pneumatic
Systems Using Low-Cost Solenoid Valves (T. Nguyen,
J.2007) [4]
By developing a simple sliding-mode control law, we
have used inexpensive components to create an
pneumatic actuation system that performs very well. We
have demonstrated that the approach only needs simple
on/off valves and a position sensors to be implemented.
Robustness is achiev with our approach due to its high
tolerance for uncertainties in the system dynamics. In
addition, the control law only switches the on/off valves
when necessary and, therefore, prolongs the valve life
and increases the overall reliability of the hardware.
A practical control strategy for servo-pneumatic
actuator systems (JihongWang 1999) [5]
The theoretical analysis reveals that the acceleration
feedback indirectly represents the cylinder chamber
pressure in difference feedback so it is possible to
employ acceleration instead of pressure feedback in the
construction of servo-pneumatic actuator control
systems. Both simulation and experimental results are
show that the role of acceleration feedback is similar of
pressure difference feedback with respect to the
stabilization of pneumatic actuator systems. A moulded
PID control strategy is described in this paper to
improve in stability of pneumatic actuator systems and
to compensate for system nonlinearities. A simple
structure is important feature of the control strategy so it
is practically feasible for industrial applications.
J. Design Specifications
Table 2. Cylinder
Table 3. Pressure Transmitter
Type Double acting Hydraulic
cylinder
Bore Diameter 80mm
Stroke Length 250mm
Cylinder Length 350mm
Force Reaches 2100KN
Piston Rod
Diameter 15mm
Supply Pneumatic
Type Silicon –on-sapphire sensor
technology
Pressure range 0-400bar to 0-4000bar
Accuracy 0.25%NLHR
Electrical
output
4-20 Ma
Temperature High operating temperature
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348
Table 4. Pressure Relief Valve
Table 5. Linear Motion Precision Potentiometer
Table 6. Motor
III. RESULTS AND DISCUSSION
Solid Works Model
A. Double Acting Cylinder
A double-acting cylinder is a cylinder in which the
working air acts alternately on both sides of the piston.
In order to connect the piston in a double-acting cylinder
to an external mechanism, such as a crank shaft, the hole
must be provided in one end of the cylinder for a piston
rod and this is fitted Double-acting with a gland or
'stuffing box' to prevent escape the working fluids.
Double-acting cylinders are common in steam engines
but unusual in the engine types. Many hydraulic and
pneumatic cylinders use them where it is needed to
produce a force in both directions. A double-acting
Pneumatic cylinder has a port at each end, supplied with
Pneumatic air for both the retraction and extension of
the piston. A double-acting cylinder is used to an
external force is not available in retract the piston or
where high force is required in both directions of travel
figure 7.
Figure 7. Double Acting Cylinder
B. FRL Units
An airline filter clean the compressed air. It strains the
air and traps in solid particles dust, dirt, rust and
separates liquids water, oil entrained in the compressed
air. Filters are installed in the air line Up stream of
regulators, lubricators, directional control valves, and air
driven devices such as cylinders and air motors. Pressure
regulators reduce and control fluid pressure in the
compressed air systems. The regulators are also
frequently referred to PRVs pressure reducing valves.
Optimally, a pressure regulator maintains a constant
output pressure regardless of variations in a input
pressure and downstream flow requirements. The
practice, output pressure is influenced to some degree by
variations in primary pressure and flow. A lubricator
adds controlled in quantities of oil into a compressed air
system to reduce the friction of moving components.
Fluid NO.6 Fuel
oil Required capacity
1,200 gal/min
Set pressure 150 psig
Over Pressure 10%
Back Pressure Atmosphere
Inlet relieving Temperature
60F
Dynamic Viscosity
850 Cp
Specific Gravity
0.993
Resistance 1.0K ohms/inch
Linearity +-0.25%
Electrical stroke 1to36 inches
Mechanical travel Electrical +1/2 inch
Power
Dissipation 1watt/inch @25c
Temperature
range -25c to 100c
Stroke Velocity Pneumatic = 20 inches/sec
Electric Motor 3hp,1440rpm,50HZ
Tank Capacity 80litres
Vane Pump Shaft Speed (750-1882)rpm
Max.175kgf/cm
Oil grade servo 68
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349
Figure 8. FRL Units
C. 5/3 DCV Valves
Directional control valves are vital in any pneumatic
circuit with directing or blocking airflow to control the
speed or sequence of operations. One method of
classifying directional-control valves is the flow paths
under various operating conditions. Important factors in
the number of possible valve positions and the number
of ports and flow paths.
Figure 9. 5/3 DCV Valves
D. ON/OFF Solenoid Valves
The two way, two position valves consist of two ports
connected in a passage that can be opened or blocked to
control flow through the valve. Usually, an electrically
activated solenoid shifts of valve spool or poppet to
direct flow. The valve provid an easy on-off function,
which many systems use to interlock, isolate, and
connect various system parts.
Figure 10. ON/OFF Solenoid Valves
E. Foot Pedal Valve
If Offered in 3- or 4-way models, these Foot Pedal
Valves are used in unlimited applications in factory
automation. Two versions are offered either a low-
profile flat pedal or a standard pedal with are without a
guard. These valves offer in operating pressure range of
0 to 150 psig, operating temperature range of 32 to
140°F and 1/4” NPT ports.
Figure 11. Foot Pedal Valve
F. Controlling The Accurate Position Of Pneumatic
Actuator Using Solenoid Valves
The source of voltage comes to control station through
serial interface 115Kps.Then the control station gives
output in 300Hz to amplifer data aquitision and PWM
drives.The aquitision give the input signal for air valve
and PID valves gives signal to position sensor to torque
sensor and send to the pressure to actuated the
pneumatic actuator.
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350
Figure 12. Controlling The Accurate Position of
Pneumatic Actuator Using Solenoid Valve
G. ON/OFF Controller For Pneumatic Actuator
Figure 13. ON/OFF Controller For Pneumatic Actuator
H. Pulse Width Modulation Controller
Figure 14. Pulse Width Modulation Controller
I. Implementing The PID Controller In Pneumatic
Actuator
Figure 15. Implementing The PID Controller In
Pneumatic Actuator
IV. CONCLUSION
A fast accurate and inexpensive position in controlled
pneumatic actuator that may be applied to a variety of
practical positioning applications was developed. The
position control was successfully implemented using
on/off solenoid valves. The valves were pulsed using a
novel PWM algorithm which produced a very linear
open-loop velocity response. The open-loop
characteristic was shown both theoretically and
experimentally to be near symmetrical, despite the
difference in the cross-sectional areas of the piston due
to the rod. A comparison of open and closed loop
responses of the standard PWM techniques and that the
novel PWM technique shows that there has been a
significant improvement in the control. A linear model
was identified for the open-loop plant from experimental
data. The model parameters obtained at mid stroke were
used in combination with manual tuning to tune a PID
controller. Coulomb friction compensation combined
with bounded integral control was found to substantially
reduce the steady-state error due to striation. The
actuator‟s accuracy was limited by the accuracy of the
potentiometer and the A/D resolution. A worst case
steady-state accuracy of 0.21mm was achieved. The
actuator can respond to commanded moves as small as
0.11 mm. Position feed forward was used to reduce the
following error to S-curve profiles. Following errors less
than 2.0 mm were achieved. The actuator‟s performance
was robust to changes in the system mass. A sixfold
increase in the mass increased the Trouble shoot in
closed loop control by 1 mm, but did not affect the rise
time or the steady-state accuracy. The actuator‟s overall
performance is comparable to that achieved by other
researchers using servo valves.
International Journal of Scientific Research in Science and Technology (www.ijsrst.com)
351
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